High-efficiency heating apparatus

ABSTRACT

A high efficiency heating apparatus for heating fluids and cooking mediums, such as oil or shortening within a fryer, includes a natural draft (non powered) combustion chamber that is affixed to an exterior surface of a fry tank.

This application is a continuation of U.S. patent application Ser. No.17/198,801, filed 11 Mar. 2021, titled “High-Efficiency HeatingApparatus,” which is a continuation-in-part of U.S. patent applicationSer. No. 16/891,868, filed 3 Jun. 2020, titled “High-Efficiency HeatingApparatus,” which issued as U.S. Pat. No. 10/966,570 on 6 Apr. 2021; andthis application is a continuation of International Application No.PCT/US2021/034547, filed 27 May 2021, titled “High-Efficiency HeatingApparatus,” which is a continuation-in-part of U.S. patent applicationSer. No. 17/173,960, filed 11 Feb. 2021, titled “High-Efficiency HeatingApparatus,” which is continuation of U.S. patent application Ser. No.16/891,868, filed 3 Jun. 2020, titled “High-Efficiency HeatingApparatus,” which issued as U.S. Pat. No. 10/966,570 on 6 Apr. 2021.International Application No. PCT/US2021/034547, filed 27 May 2021,titled “High-Efficiency Heating Apparatus,” is also acontinuation-in-part of U.S. patent application Ser. No. 17/198,801,filed 11 Mar. 2021, titled “High-Efficiency Heating Apparatus.”

BACKGROUND Field of the Invention

The present application relates to deep fryers. In particular, thepresent application relates to a natural draft combustion system fordeep fryers.

Description of Related Art

There are millions of deep fryers in use throughout the world. They arefound in almost every restaurant and commercial kitchen. Deep fryers aredesigned for quickly cooking deep-fried foods, including, but notlimited to, French fries, chicken cutlets, fried vegetables, fried fish,fried ice cream, etc. Deep fryers generally include: (1) a cookingvessel or fry pot within which a cooking medium such as oil orshortening is heated to appropriate temperature for cooking; (2) a heatsource, including gas, such as natural gas or propane, and electricity;(3) a control system for controlling the heat input to the cookingmedium; and (4) a drain system for draining the cooking medium foreither disposal or filtering and return to the cooking vessel. As withmany commercial appliances, the size and shape, i.e., the footprint, ofthese deep fryers has been standardized to aid in their design,installation, maintenance, and replacement.

Gas powered deep fryers typically include tube and open tank designs.Tube fryers transfer heat to the oil contained within the cooking vesselvia tubes that pass into, throughout, and then exit the cooking vessel.The combustion systems associated with tube fryers include natural draftkits, pulse combustion, and powered burners—both forced and induceddraft. Depending on the combustion system and the heat transferconfiguration of the tubes, the efficiency of tube fryers may range fromapproximately 30% efficiency to approximately 55+% efficiency.

However, tube fryers have several drawbacks. The heat exchange tubesreside in the cooking vessel causing cleaning and maintenance issues.Users must brush and clean around and under the tubes. Additionally,food products from the cooking process drop onto the hot tubes, burningand charring the food, thereby degrading the cooking oil. Lastly, thetubes and the walls of the cooking vessel experience thermal expansion,but at different rates. Because of this, cracks can develop in andaround the welds where the tubes enter and exit the cooking vessel, aswell as at other places, causing leaking and reliability/maintenanceproblems.

On the other hand, open tank fryers achieve heat or energy transfer fromthe combustion process through the side walls of the cooking vessel tothe oil. The principal advantage of open tank fryers is that no heatexchange tubes pass through the cooking vessel and therefore do notreside within the cooking oil. Open tank fryers provide unobstructedaccess to the tank's interior making cleaning substantially easier,eliminating degradation of the cooking oil due to charring, andeliminating the reliability issues associated with broken welds. Opentank fryers are generally cheaper to manufacture and offer ease ofcleaning and better/longer oil life as compared to tube fryers. Liketube fryers, the combustion systems of open tank fryers range fromnatural draft to powered types with similar efficiencies. Low-cost,conventional natural draft open tank fryers are generally about 30%efficient (low efficiency). High efficiency open tank fryers haveefficiencies approaching 55%.

High efficiency tube and open tank fryers have drawbacks. The maindrawback of high efficiency open tank fryers include the high cost tomove hot combustion gas, due to the sophisticated controls, poweredburners (featuring either forced draft combustion blowers or induceddraft fans), and infrared burners, because these complex features addcost and contribute to reliability and maintenance issues. For highefficiency tube fryers, heat exchange designs have become much moreintricate, using complex tube designs (longer tubes, bends, varyingcross-section) or finned heat exchangers to extract more energy from thecombustion gases.

Hence, there is a need for a highly efficient open tank fryer with asimple, reliable, and inexpensive natural draft combustion system thatfits within the footprint of conventional deep fryers.

DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are setforth in the appended claims. However, the invention itself, as well asa preferred mode of use, and further objectives and advantages thereof,will best be understood by reference to the following detaileddescription when read in conjunction with the accompanying drawings,wherein:

FIG. 1 is a perspective view of a deep fryer, according to the presentapplication;

FIG. 2 is a partial cross section of the deep fryer of FIG. 1 taken atII-II;

FIG. 3 is a partial cross section of the deep fryer of FIG. 1 taken atIII-III;

FIG. 4 is a partial perspective view showing a right sidewall and onecombustion chamber of the deep fryer of FIG. 1 ;

FIG. 5A is a partial cross section (as seen from above) of a burnerassembly and a flame front of the deep fryer of FIG. 1 ;

FIG. 5B is a partial cross section (as seen from the right side) of aburner assembly and a flame front of the deep fryer of FIG. 1 ;

FIG. 6 is an upward partial perspective view illustrating combustionchambers, burners, and insulation of the deep fryer of FIG. 1 ;

FIG. 7 is a side partial perspective view illustrating a taperedcombustion chamber, a burner assembly, and baffles, according to thepreferred embodiment of the deep fryer of the present application;

FIG. 8A is a partial cross section (as seen from above) illustrating aradially tapered combustion chamber, a burner, a flame front, andbaffles, according to an alternative embodiment of the deep fryer of thepresent application;

FIG. 8B is a partial cross section (as seen from above) illustrating aradially tapered combustion chamber, a burner, a flame front, andalternate flow tabs or vanes, according to another alternativeembodiment of the deep fryer of the present application;

FIG. 9 is a partial cross section (as seen from the right side) of analternative embodiment of the deep fryer of the present application;

FIG. 10 is a partial right side view of an alternative embodiment of adeep fryer according to the present application;

FIG. 11 is a partial cross-sectional view of the deep fryer of FIG. 10taken along Section A-A of FIG. 10 ;

FIG. 12 is a partial right side view of another alternative embodimentof a deep fryer according to the present application; and

FIG. 13 is a partial cross-sectional view of the deep fryer of FIG. 12taken along Section A-A of FIG. 12 .

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As used herein, the terms “fryer,” “deep fryer,” “deep-fat fryer,” “tankfryer,” “commercial floor fryer,” and “floor fryer” have the samemeaning and refer to cooking apparatus generally having four subsystems,including: (1) a cooking vessel or fry pot within which a cookingmedium, such as oil, shortening, or water is heated to appropriatetemperature for cooking, (2) a heat source, including gas, such asnatural gas or propane, and electricity, (3) a control system forselectively controlling the heat input to the cooking medium, and (4) adrain system for use in draining the cooking medium for either disposalor filtering and return to the deep fryer. Also, as used herein, theterms “vessel,” “cooking vessel,” “open pot,” and “fry pot” have thesame meaning and refer to the reservoir in a deep fryer in which thecooking medium resides. In addition, although the heating apparatus ofthe present application is described with respect to a deep fryer, itwill appreciated that the heating apparatus may be used for othercooking and heating applications. For example, the heating apparatus ofthe present application may be used as a pasta cooker or other boiler,in which the cooking medium is water, seasoned water, steam, broth, etc.In such applications, the heating and cooking parameters describedherein may be altered or modified without departing from the spirit ofthe present application.

As used herein, the term “tube fryer” refers to a deep fryer having acooking vessel that transfers heat into a cooking medium contained bythe cooking vessel via combustion tubes that pass into, run through, andexit the cooking vessel. In contrast, as used herein, the term “opentank fryer” refers to a deep fryer in which heat or energy istransferred from the combustion process through the side walls of thecooking vessel to the cooking medium.

As used herein, the term “gas” refers to natural gas, propane, and allother petroleum-based and/or ignitable combustion sources. Thus, theterm “gas” is not meant to be limiting but is inclusive of anyappropriate combustion source. Also, as used herein, the terms “naturaldraft system” and “natural draft combustion system” have the samemeaning and refer to systems in which the motive force to induce theflow of the combustion gasses is achieved via the natural pressuredifferential between the hot gasses and the surrounding atmosphericcondition. The resulting buoyancy force is sufficient to transport theproducts of combustion through the combustion and heat exchange zoneswithout requiring additional pressure or flow control sources, such asblowers or fans.

As used herein, the term “commercial” refers to all foodservice venuesincluding, but not limited to, large chain operations and individualoperators selling food product directly to the consumer.

The problems associated with conventional deep fryers, both open potfryers and tube fryers, are solved by the principles and conceptsembodied by the high efficiency heating apparatus of the presentapplication.

Referring to FIG. 1 in the drawings, an open tank, gas-combustion deepfryer 8 according to the present application is illustrated. Deep fryer8 includes a rectangular metal housing 10 forming an enclosure for a frytank 12. Housing 10 preferably includes a left sidewall 16, a rightsidewall 17, a back wall 18, an angled shelf 11, and a front wall 19.Front wall 19 houses controls 20, and is preferably removable and/orhinged to allow access to control wiring and other apparatus withinhousing 10.

Deep fryer 8 is an open tank natural draft (non-powered) gas-combustionfryer. Deep fryer 8 is a high-efficiency, low-cost, heating apparatusfor heating fluids and cooking mediums, such as oil or shortening. Deepfryer 8 is particularly well suited for commercial restaurant cooking,and for preparing deep-fried foods, including, but not limited to,French fries, fried ice cream, chicken cutlets, fried vegetables, friedfish, etc.

Although deep fryer 8 may be manufactured in any size, shape, anddimensions, dependent upon the desired use and application, in thepreferred embodiment, deep fryer 8 does not increase the volumetricspace requirements of conventional deep fryers. Thus, deep fryer 8 ispreferably configured to fit within the same “footprint” as conventionaldeep fryers. As such, deep fryer 8 preferably utilizes between 35-50pounds of cooking oil or other cooking medium. In a preferredembodiment, the input rate of the deep fryer 8 is 24.6 kW (or 84,000Btu/hr). Alternatively, deep fryer 8 may be configured for industrialand automated applications.

Referring now also to FIGS. 2 and 3 in the drawings, fry tank 12 issized to hold one or more baskets 21 and a cooking medium 22, such asoil or shortening. In the preferred embodiment, deep fryer 8 is a floorfryer, wherein fry tank 12 is configured to hold between 35-50 pounds ofcooking medium 22, has a cooking volume of approximately 14 inches wide,by 14 inches long, and 6 inches deep. Preferably, the volume of fry tank12 is used to hold two or more food product baskets 21.

Alternatively, deep fryer 8 may be configured as a low volume fryer(LVF). In the LVF embodiment, deep fryer 8 has a smaller excess oilcapacity than the preferred embodiment. However, in the LVF embodiment,deep fryer 8 is configured with enough oil capacity for the desiredcooking load, recovery time, and drag out (the oil consumed duringcooking). The volume of fry tank 12 in the LVF embodiment is preferablycapable of holding approximately less than or equal to 35 pounds ofcooking medium 22. The reduction in oil capacity results in oil savingsfrom reducing waste oil and oil life extension. The savings from thereduced oil and oil waste can be substantial.

Referring now also to FIGS. 2-6 in the drawings, fry tank 12 includes alower chamber 30, a transition zone 42, and a cooking zone 43. Cookingzone 43 is in fluid connection with transition zone 42 and lower chamber30. Lower chamber 30 is comprised of opposed front and back walls 32,34, opposed left and right walls 36, 38, a bottom wall 39, and a largediameter oil drain 40. Preferably, front and back walls 32, 34 and leftand right walls 36, 38 are substantially vertical and straight, whilethe bottom wall 39 is curved. However, slight variations in linearity,curvature, and orientation of the walls will be recognized asalternative embodiments and are encompassed in the present application.

Bottom wall 39 forms a cold zone 45 and is configured and dimensioned toallow quick and easy hand cleaning. Cold zone 45 is located below lowerchamber 30 and is a relatively cool and quiescent zone compared to thebulk of the oil in the remainder of fry tank 12, which has a set pointtypically in the range of 325-375° F. Collection of food particles incold zone 45 is desirable because charred food degrades the cooking oil,thereby reducing the life of the oil. In general, a larger cold zone 45is preferred, especially for battered products, but practical designlimitations such as overall tank volume, energy needs, and minimizationof the oil volume used for the cooking process, requires this volume toremain small.

Transition zone 42 includes angled walls 52, 54. Cooking zone 43includes opposed side walls 44, 46, which preferably are substantiallyvertical, a front wall 48, and a back wall 50. Left and right walls 36,38 of lower chamber 30 are connected to respective side walls 44, 46 ofcooking zone 43 by the respective angled walls 52, 54 of transition zone42. The gas-combustion process results in heating of the cooking medium22 and occurs primarily at sidewalls 36, 38 of lower chamber 30. Heatedair and other by-products of the combustion process are in fluid contactwith the outer surface of walls 36, 38 of lower chamber 30.

Deep fryer 8 is an open tank deep fryer having a natural draft(non-powered) gas-combustion system 67. Non-powered natural draftgas-combustion system 67 includes a gas supply conduit 72, at least onenozzle 68 in fluid communication with gas supply conduit 72, a jet 70 influid communication with nozzle 68, an angled burner 66 in fluidcommunication with jet 70, a fixed element, such as an inlet air plate73 or other flow control device, coupled to, operably associated with,or connected to angled burner 66, a combustion chamber 60 in fluidcommunication with burner 66, and an igniter 80. As is shown, combustionchambers 60 are located entirely outside of fry tank 12. Thisdistinguishes the present application from tube fryers, in which thecombustion tubes are disposed within the fry tank.

The fixed element is preferably disposed at or near the entrance tocombustion chamber 60. This location may also be referred to as upstreamof combustion chamber 60. One reason for the fixed element disposed ator near the entrance, i.e., upstream of combustion chamber 60 is togenerate a focused secondary airflow needed/desired for turbulent flowin the combustion zone. It is preferred that the flow of the secondaryair be managed, i.e., velocity/magnitude and direction, and flowrate, atthe entrance to combustion chamber 60. It is possible to restrict thesecondary airflow upstream of combustion chamber 60, but it is stilldesirable to direct the secondary air flow into combustion chamber 60and this happens preferably at the entrance to combustion chamber 60.

Burner 66 terminates at a burner face 75, which may be disposed justwithin combustion chamber 60 or disposed adjacent combustion chamber 60in a manner that allows for a small separation between burner face 75and combustion chamber 60. In either configuration burner 66 is in fluidcommunication with combustion chamber 60. It will be appreciated that inthose embodiments of the present application in which multiplecombustion chambers 60 and multiple burners 66 are employed, gas supplyconduit 72 may serve as a manifold for distributing gas between themultiple combustion chambers 60 and burners 66.

Gas is supplied to gas supply conduit 72 and thereafter flows throughnozzles 68 to gas jets 70, where the gas mixes with air and thereafterflows down angled burners 66 to inlet air plates 73 and igniter 80.Igniter 80 causes the pre-mixed gas to combust, producing a selectivelyangled flame front 81. To aid with complete combustion, secondary air isintroduced into the combustion process through secondary air openings 74in inlet air plate 73. Preferably, deep fryer 8 includes one manifold 72on each side of lower chamber 30, with each manifold 72 servicing threenozzles 68, three jets 70, three burners 66, three air inlet plates 73,and three combustion chambers 60.

In the preferred embodiment, lower chamber 30 has left and right walls36, 38 dimensioned at approximately 1.0-1.5 ft², resulting in a totalside heat transfer area of two to three square feet. The required heatinput to left and right walls 36, 38 is achieved by both convection andradiation from combustion system 67, with radiation providingapproximately one-third of the total heat transfer, and convectionproviding the remaining heat transfer. Each of left and right walls 36,38 transfers between about 5 kW to 9 kW (or 20,000 to 30,000 Btu perhour) to the cooking oil under heavy cooking conditions.

To further optimize heat transfer, the exterior walls of each combustionchamber 60 are covered with one or more layers of high temperatureinsulating material 64. Insulating material 64 has low thermalcapacitance and high heat transfer resistance, but is neverthelesscompact to fit within the footprint of deep fryer 8. Preferably, thethermal profile of each combustion chamber 60 is maintained usinginsulating material 64, so that each combustion chamber 60 does notrevert to the mean wall temperature of lower chamber 30. Reverting tothe mean wall temperature of lower chamber 30 greatly reduces radiationto fry tank 12 given the quadratic heat transfer relationship oftemperature (e.g., q″(W/m²)=εσ(T⁴ _(s)-T⁴ _(sur))).

Referring now specifically to FIG. 4 in the drawings, one possibleassembly method for combustion chamber 60 is illustrated. Combustionchambers 60 are affixed to left and right walls 36, 38 of lower chamber30. Each combustion chamber 60 extends substantially horizontally fromfront wall 32 to back wall 34, having an inlet portion 56 and an outletportion 58. Each combustion chamber 60 is preferably a C-shapedrectangular enclosure attached to either left wall 36 or right wall 38of lower chamber 30. By way of example, if only one combustion chamber60 is utilized, combustion chamber 60 will be a three-sided C-shapedenclosure with either left wall 36 or right wall 38 forming the fourthside when combustion chamber 60 is affixed thereto. In the eventmultiple combustion chambers 60 are utilized on each side of fry tank12, each combustion chamber 60 will have three interior surfaces withthe fourth side formed by the aforementioned left and right walls 36,38. Various manufacturing processes may be employed and as such multiplechambers may share an interior wall. The rectangular combustion chamber60 is sealed, except at the inlet and outlet, such that hot gas flowingthrough each combustion chamber 60 is confined within such combustionchamber 60. Additionally, various configurations may be utilized inaddition to the C-shaped configuration. For example, combustion chamber60 may be configured as a semicircle or semi-ellipse shaped chamber withthe open portion affixed to left or right wall 36, 38.

Each outlet portion 58 of chamber 60 is in fluid communication with anexhaust conduit, or flue 35 (see FIGS. 1 and 3 ). In the preferredembodiment, six combustion chambers 60 are affixed to lower chamber 30,with three combustion chambers 60 on each of left and right walls 36,38. This description is meant to be illustrative and not limiting, asdeep fryer 8 may be practiced with more or less than six combustionchambers 60. For example, with the LVF embodiment, fewer and/or smallercombustion chambers 60 may be utilized.

For higher temperature operation and quick response, each combustionchamber 60 is preferably made of a thin-walled, high-temperature metalsuch as Inconel®, which is both durable and cost effective.Alternatively, cast ceramic enclosures, or a segmented high-temperaturemetal liner are also options. Preferably, the height of each combustionchamber 60 is approximately two inches, causing tight radiation couplingbetween left and right walls 36, 38 of fry tank 12 and combustionchamber 60. However, other heights, including one, three, four, fiveinches, and more are also encompassed by the present application. Thehigh-temperature insulating material 64 surrounding combustion chambers60 maintains the primary heat transfer zone in excess of 1,000° F.Preferably, insulation material 64 comprises a high-temperature aerogelinsulation that minimizes heat loss to the surrounding areas andmaintains the outer walls of combustion chambers 60 at the hightemperature required for a desired radiative heat transfer betweencombustion chambers 60 and left and right walls 36, 38.

Referring now specifically to FIGS. 5A and 5B in the drawings, theunique configuration and function of angled burners 66, burner faces 75,and flame front 81 are depicted. In the preferred embodiment, eachburner face 75 has an area of approximately one-inch wide bythree-inches high and a firing rate of approximately 3 kW to 5 kW (or12,000 to 14,000 Btu/hr), with a combustion heat release volume that isin excess of 50 in³. Preferably, each nozzle 68 is operated at apressure of 3.5 inches water column, enabling each nozzle 68 to entrain50-60% of the primary air. Preferably, the length of the body of eachburner 66 is six to seven inches, allowing for good mixture of fuel flowand primary air. Due to the amount of primary air entrained, arelatively compact primary flame is produced with secondary airintroduced around the perimeter of the burner face 75. Preferably,secondary inlet air plate 73 controls the amount of secondary airintroduced to the flame. Preferably, pre-mixed gas and air is introducedinto burner 66 and ignited by ignition source 80. Thereafter, secondaryair introduced to burner 66 through secondary air openings 74 allowingcomplete combustion.

Burner 66 is configured with a downward directed angle allowing theprimary air/gas mixture to flow down burner 66 to the substantiallyvertical burner face 75 and thereafter contact the bottom wall ofcombustion chamber 60 at a downward directed angle (see FIG. 5B). Thisdownward angle of flame front 81 is generally due to the momentum of thegas flow. This unique selective angling of flame front 81 helpscombustion chamber 60 remain as hot as possible, while maintaining amaximum temperature profile. The downward directed angle of burner 66,and the resulting downward directed flame front 81 causes greatercontact of the flow of the hot combustion gasses with the bottom ofcombustion chamber 60, resulting in a longer residence time and therebyenhancing heat transfer to the cooking medium 22.

Alternatively, burner 66 may be configured with an upward directed angleallowing the primary air/gas mixture to flow down burner 66 to thesubstantially vertical burner face 75 and thereafter contact the topwall of combustion chamber 60 at an upward directed angle. Thisconfiguration of upward directed angle for burner 66 is shown in theembodiment of FIG. 10 . This upward directed angle of flame front 81 isgenerally due to the momentum of the gas flow. The selective angling offlame front 81 helps combustion chamber 60 remain as hot as possible,while maintaining a maximum temperature profile. The upward directedangle of burner 66, and the resulting upward directed flame front 81,causes greater contact of the flow of the hot combustion gasses with thetop of combustion chamber 60, resulting in a longer residence time,thereby enhancing heat transfer to cooking medium 22.

Various other angles of orientation of burner 66 may be utilized inorder to enhance heat transfer to cooking medium 22. Thus, by disclosinga downward and an upward angle of flame front 81 applicant does notintent to limit the directed angle of flame front 81 possibilities ofburner 66.

Convection and radiation from the products of combustion provide theheat transfer to left and right walls 36, 38 of lower chamber 30. Asused herein, the “burner tilt angle” is defined as the included anglebetween a normal vector from burner face 75 to the surface (e.g.,vertically disposed, side surface) of left and right walls 36, 38adjacent to burner face 75. A burner tilt angle of zero degreesindicates that the combustion process is occurring parallel to walls 36,38. For a burner tilt angle greater than zero degrees, flame front 81 isin close contact with right and left walls 36, 38.

Ignited combustion gas is directed toward left and right walls 36, 38via burner 66 at a burner tilt angle of greater than zero degrees shownin top view FIG. 5A. Burner 66 is tilted according to a selected burnertilt angle towards walls 36, 38, such that hot gas from a turbulentcombustion process is in close contact with left and right walls 36, 38.Flame front 81 for burner tilt angles between 5° and 15° can achievecomplete combustion and also “adhere” to left and right walls 36, 38,producing higher convective heat transfer rates. FIG. 5A illustrates aburner tilt angle greater than zero degrees.

Referring again to FIG. 3 , the combustion chamber 60 is biased upwardfrom a horizontal axis at a draft angle 62. The upward draft angle isgreater than zero degrees from the horizontal axis and promotesefficient combustion during start-up conditions when flue 35 isrelatively cold. Draft angle 62 enables a small positive draft andpromotes the flow of the hot gases by increasing the buoyancy effect.Although a draft angle greater than zero degrees and less than 15degrees is preferred, because these angles promote a small positivedraft, draft angles greater than 15 degrees may be utilized.

Combustion chamber 60 has three separate zones or areas: a combustionzone 90, a first heat transfer zone 95, and a second heat transfer zone98. Combustion zone 90 provides sufficient volume for primary andsecondary gas combustion. Burner 66 is a partially premixed burner,using less than 100% stoichiometric air. Thus, the primary combustionair is mixed with a gaseous fuel upstream of combustion zone 90. Inburner 66, primary air levels set the rate of combustion and thereforedefine the general combustion volume and shape. To drive the combustionreaction to completion for burner 66, additional secondary air isintroduced into the combustion volume. In general, secondary air issupplied to the combustion process in amounts exceeding 100-150% ofstoichiometric requirements.

The combustion process is accomplished via flame front 81 having a shortcompact flame from burner 66, with a majority of the combustion processaccomplished in combustion zone 90 within the first approximately 20% ofthe length of the combustion chamber 60. This permits maximum contact ofthe hot gasses to walls 36, 38. The combustion zone is the volume withincombustion chamber 60 associated with the combustion gas. The size andshape of the combustion zone are determined by the fuel input rate,primary air levels, secondary air levels, and mixing efficiency.

Only a portion of the total convection heat exchange occurs withincombustion zone 90. Directed gas from the combustion zone 90 next entersfirst heat transfer zone 95. First heat transfer zone 95 isapproximately 50-60% of the length of combustion chamber 60. One or morebaffle systems 100 (see FIGS. 7, 8A, and 8B) direct hot gas flow around,through, and towards left and right walls 36, 38. Baffle systems 100 area high temperature component, generally made of metal, and are heated tored to white hot by the combustion gas flow producing both convectionand radiation heating to left and right walls 36, 38. Various baffleconfigurations may be employed to accomplish hot gas flow to left andright walls 36, 38. Baffle systems 100 are located just beyondcombustion zone 90, approximately midway through combustion chamber 60,and are designed so that baffle systems 100 do not inhibit thecombustion process. Hot gas flow directed by baffle systems 100 operatesat temperatures in excess of 1,100° F.,

FIGS. 8A and 8B present two such illustrative baffle designs. The baffleconfigurations are tightly coupled to enclosure geometry, flame and/orcombustion characteristics, and burner angle. To “grab” and direct gasflow in a low loss manner, baffle systems 100 preferably use a series offlow tabs or vanes 112. Vanes 112 are positioned to both route the hotgases through baffle systems 100 as well as direct portions of the flowtoward left and right walls 36, 38. Baffle systems 100 operate in a hotportion of the gas flow and will approach the gas flow temperature andact as a very effective radiation source to fry tank 12. Baffle systems100 may be configured from a single sheet of material 101, as shownschematically in FIG. 8A, or may be configured from separate individualsheets of material 103, as show schematically in FIG. 8B.

Combustion gas that flows through combustion chamber 60 begins to coolas it passes baffle system 100 with the combustion chamber walltemperature profile decreasing from approximately 1,100° F., or more, toapproximately 550° F., or more, prior to outlet portion 58. The taperingof the combustion chamber 60 (see FIG. 7 ) reduces the cross section ofcombustion chamber 60 and forces the hot outer wall of combustionchamber 60 closer to left and right walls 36, 38, thereby increasingheat transfer coupling. The spent gas then exits combustion chamber 60and enters flue 35. Without tapering, the velocity of combustion gassesdecreases over the length of combustion chamber 60. A combustion chamberwith a constant cross-sectional area will experience an undesirablereduction in local convective heat transfer with cooling flows. Theincrease in local flow densities with gas cooling and the resultingdecrease in bulk flow velocity results in lower local heat transfer.Tapering combustion chamber 60 increases local flow velocities,improving the local convective heat transfer coefficient.

Burner 66 may be held in place by an indexing tab 59. As shown in FIGS.8A and 8B in the drawings, the tapering of combustion chamber 60 inthese embodiments is curved. Convection heat exchange occurs incombustion zone 90 of combustion chamber 60, radiant and convection heatexchange occurs in first heat transfer zone 95, and heat transfer in theform of convection occurs in second heat transfer zone 98. As is shown,combustion zone 90 is approximately 20% of the length of combustionchamber 60, first heat transfer zone 95 is approximately 50-60% ofcombustion chamber 60, and second heat transfer zone 98 is approximately20-30% of the length of combustion chamber 60. Spent gas exitscombustion chamber via outlet portion 58 and into flue 35. Flue 35 isthe collection point for hot gas leaving combustion chamber(s) 60 andexhausts spent gas from deep fryer 8 to atmospheric venting. Although amajority to nearly all the heat transfer to fry tank 12 occurs withincombustion chamber 60, a small amount of beneficial heat transfer occursbetween lower chamber 30, back wall 34, and flue 35.

Referring now also to FIGS. 6, 7, 8A, and 8B, alternative configurationsfor combustion chamber 60 are illustrated, both externally (FIGS. 7, 8A,8B) and non-externally (FIG. 6 ) tapered embodiments. Combustion chamber60 preferably has a length 102 of approximately 12-14 inches, a height104 of approximately 1-1.5 inches, and a width (for tapered embodimentsshown in FIGS. 7, 8A and 8B), 108 of approximately 2 inches, where thewidth dimension is relative to the combustion chamber width at inletportion 56. For externally tapered embodiments, the width 108 tapers toapproximately 1-1.5 inches at outlet portion 58.

Various methods of tapering or reducing combustion chamber 60 volume maybe utilized. For example, a radial tapering (see FIGS. 8A and 8B), anangled tapering (see FIG. 7 ), or combinations thereof may be used totaper combustion chamber 60. While the described examples are providedfor illustrative purposes, other tapering methods may be employed andare encompassed by the present application. For example, an adjustableor fixed deflector 125 may be installed within, or at least partiallywithin, combustion chamber 60, thereby reducing the volume of chamber60. Adjustable deflector 125 (see FIG. 6 ) may be coupled with thecontrol system of deep fryer 8 and may be configured to open or closedepending upon performance desires and/or programming. Alternatively,deflector 125 may be manually controlled. Although combustion chamber 60of FIG. 6 , i.e., having a constant cross-sectional area, functionswell, the angled tapered combustion chamber 60 of FIG. 7 , i.e., havinga selectively reduced cross-sectional area, is preferred for deep fryer8. The pressure available due to tapering is not overly restrictive anddoes not choke or reduce the secondary air flow.

The natural draft combustion system of the present application providessignificant advantages including, but not limited to: 1) elimination ofheat exchange tubes passing through a fry tank; 2) elimination ofreliability and maintenance issues associated with tubes in a fryer; and3) elimination of expensive control systems, blower fans, and othermeans required in existing powered high efficiency open pot fryers.

Referring now to FIG. 9 in the drawings, an alternative embodiment of adeep fryer 8′ according the present application is illustrated. In thisembodiment, combustion chambers 60′ are generally vertically orientedbetween a front wall 48′ and a back wall 50′. Deep fryer 8′ includes afry tank 12′ that is sized to hold one or more baskets 21′ and a cookingmedium 22′, such as oil or shortening. Deep fryer 8′ is a floor fryer,wherein fry tank 12′ is configured to hold between 35-50 pounds ofcooking medium 22′, has a cooking volume of approximately 14 incheswide, by 14 inches long, and 6 inches deep. Preferably, the volume offry tank 12′ is used to hold two or more food product baskets 21′.

Deep fryer 8′ is an open tank deep fryer having a natural draft(non-powered) gas-combustion system 67′. Non-powered natural draftgas-combustion system 67′ includes a gas supply conduit 72′, at leastone nozzle 68′ in fluid communication with gas supply conduit 72′, a jetor pump 70′ in fluid communication with nozzle 68′, a generally verticalburner 66′ in fluid communication with jet 70′, an inlet air plate 73′connected to burner 66′, a combustion chamber 60′ in fluid communicationwith burner 66′, and an igniter 80′. Burner 66′ terminates at a burnerface that is disposed just within combustion chamber 60′ or disposedadjacent combustion chamber 60′ in a manner that allows for a smallseparation between burner face 75′ and combustion chamber 60′. In eitherconfiguration, burner 66′ is in fluid communication with combustionchamber 60′. Gas is supplied to gas supply conduit 72′ and thereafterflows through nozzle 68′ to gas jet 70′, where the gas mixes with airand thereafter flows up burner 66′ to inlet air plate 73′ and igniter80′. Igniter 80′ causes the pre-mixed gas to combust, producing agenerally vertical flame front 81′. To aid with complete combustion,secondary air is introduced into the combustion process throughsecondary air openings in inlet air plates 73′. Preferably, deep fryer8′ includes one manifold 72′ on each side of a lower chamber 30′, witheach manifold 72′ servicing three nozzles 68′, three jets 70′, threeburners 66′, three inlet air plates 73′, and three combustion chambers60′.

Hot combustion gas moves through combustion chambers 60′, interacts withbaffle systems 100′ and may be affected by tapering or deflecting aspreviously described, before rising and collecting in horizontalcollection chamber 121 which is in fluid connection with a flue 35′.Alternatively, combustion chambers 60′ may be configured as narrowchannels without tapering and/or deflecting because the motive forcenecessary to move the hot gasses through chambers 60′ and intocollection chamber 21 is accomplished due to the natural vertical assentof the hot gasses (hot air rising). Collection chamber 121 is affixed totransition walls 52′, 54′. Although combustion gas entering collectionchamber 121 is cooling, it may nevertheless provide secondary heatdirectly to transition walls 52′, 54′.

Referring now to FIGS. 10-13 in the drawings, two additional alternativeembodiments of the present application are illustrated. FIGS. 10 and 11depict a open tank natural draft (non-powered) gas-combustion deep fryerhaving a lower chamber with generally vertical side walls, in which thecombustion chambers are recessed into the side walls. FIGS. 12 and 13depict a open tank natural draft (non-powered) gas-combustion deep fryerhaving a lower chamber with angled side walls, in which the combustionchambers are recessed into the angled side walls. The deep fryersdepicted in FIGS. 10-13 are similar in form, function, operation, andefficiency to deep fryer 8 of FIGS. 1-8B. As such, although utilized inthe embodiments of FIGS. 10-13 , not all of the components of deep fryer8 are shown and described here with respect to these embodiments.

In the embodiment of FIGS. 10 and 11 , a deep fryer 308 includes arectangular metal housing forming an enclosure for a fry tank 312. Thehousing preferably includes a left side wall, a right side wall, a backwall, an angled shelf 311, and a front wall. The front wall housescontrols, and is preferably removable and/or hinged to allow access tocontrol wiring and other apparatus within the housing. Deep fryer 308 isa high-efficiency, low-cost, heating apparatus for heating fluids andcooking mediums, such as oil or shortening. Fry tank 312 is sized tohold one or more baskets 321 and a cooking medium 322, such as oil orshortening. As with deep fryer 8, deep fryer 308 may be configured as alow volume fryer (LVF).

Fry tank 312 includes a lower chamber 330, a transition zone 342, and acooking zone 343. Cooking zone 343 is in fluid connection withtransition zone 342 and lower chamber 330. Lower chamber 330 iscomprised of opposed front and back walls 332, 334, opposed left andright walls 336, 338, a bottom wall 339, and a large diameter oil drain340. Preferably, front and back walls 332, 334 and left and right walls336, 338 are substantially vertical, while bottom wall 339 is curved.Bottom wall 339 forms a cold zone 345 and is configured and dimensionedto allow quick and easy hand cleaning. Cold zone 345 is located belowlower chamber 330 and is a relatively cool and quiescent zone comparedto the bulk of the oil in the remainder of fry tank 312.

Transition zone 342 includes angled walls 352, 354. Cooking zone 343includes opposed side walls 344, 346, which preferably are substantiallyvertical, a front wall 348, and a back wall 350. Left and right walls336, 338 of lower chamber 330 are connected to respective side walls344, 346 of cooking zone 343 by the respective angled walls 352, 354 oftransition zone 342. The gas-combustion process results in heating ofthe cooking medium 322 and occurs primarily at side walls 336, 338 oflower chamber 330. Heated air and other by-products of the combustionprocess are in fluid contact with the outer surface of side walls 336,338 of lower chamber 330.

Deep fryer 308 is an open tank deep fryer having a natural draft(non-powered) gas-combustion system 367. Non-powered natural draftgas-combustion system 367 includes a gas supply conduit 372, at leastone nozzle 368 in fluid communication with gas supply conduit 372, a jet370 in fluid communication with nozzle 368, an angled burner 366 influid communication with jet 370, an inlet air plate 373 connected toangled burner 366, a combustion chamber 360 in fluid communication withburner 366, and an igniter. Burner 366 terminates at a burner face,which may be disposed just within combustion chamber 360 or disposedadjacent combustion chamber 360 in a manner that allows for a smallseparation between the burner face and combustion chamber 360. In eitherconfiguration, burner 366 is in fluid communication with combustionchamber 360. It will be appreciated that when multiple combustionchambers 360 and multiple burners 366 are employed, gas supply conduit372 may serve as a manifold for distributing gas between the multiplecombustion chambers 360 and burners 366.

In the embodiment of FIGS. 10 and 11 , burners 366 are angled upward. Inaddition, burners 366 may also be angled inwardly toward the exteriorsurfaces of left and right walls 336, 338 of lower chamber 330. However,it will be appreciated that burners 366 may be angled downwardly and/orinwardly, as with burners 66. Gas is supplied to gas supply conduit 372and thereafter flows through nozzles 368 to gas jets 370, where the gasmixes with air and thereafter flows up angled burners 366 to inlet airplates 373 and the igniter. The igniter causes the pre-mixed gas tocombust, producing a selectively upwardly angled flame front 381 similarto flame front 81. To aid with complete combustion, secondary air isintroduced into the combustion process through secondary air openings374 in inlet air plate 373. Preferably, deep fryer 308 includes onemanifold 372 on each side of lower chamber 330, with each manifold 372servicing three nozzles 368, three jets 370, three burners 366, threeair inlet plates 373, and three combustion chambers 360.

To further optimize heat transfer, the exterior walls of each combustionchamber 360 are covered with one or more layers of high temperatureinsulating material. The insulating material has low thermal capacitanceand high heat transfer resistance, but is nevertheless compact to fitwithin the footprint of deep fryer 308. Preferably, the thermal profileof each combustion chamber 360 is maintained using insulating material364, so that each combustion chamber 360 does not revert to the meanwall temperature of lower chamber 330. Reverting to the mean walltemperature of lower chamber 330 greatly reduces radiation to fry tank312 given the quadratic heat transfer relationship of temperature (e.g.,q″(W/m²)=εσ(T⁴ _(s)-T⁴ _(sur))).

Combustion chambers 360 are affixed to left and right walls 336, 338 oflower chamber 330. Each combustion chamber 360 extends substantiallyhorizontally from front wall 332 to back wall 334, having an inletportion 356 and an outlet portion 358. Combustion chamber 360 is sealed,except at the inlet and outlet, such that hot gas flowing through eachcombustion chamber 360 is confined within such combustion chamber 360.

As used herein the term “wetted area” refers to a surface in heatexchange relationship with cooking medium 322. In this embodiment,combustion chambers 360 are recessed within side walls 336, 338, therebypartially enclosing combustion chambers 360. Although combustionchambers 360 are shown substantially horizontal from front wall 332 toback wall 334 in FIG. 10 , combustion chambers 360 may also be tiltedupward from a horizontal axis at a selected draft angle greater thanzero degrees, such as draft angle 62 in FIG. 3 .

As shown in FIG. 11 , side walls 336, 338 are angled and curved adjacentcombustion chambers 360, which allows for the recessing of combustionchambers 360 into lower chamber 330, thereby increasing the wetted areaat sidewall portions 386, 387, 388, and 389. Additionally, the formingof side walls 336, 338 to partially recess combustion chambers 360,increases the heat transfer wetted perimeter of combustion chambers 360with the added benefit of reducing the external sidewall areas ofcombustion chambers 360. As is shown, the areas of combustion chambers360 which are in direct contact with sidewalls 336, 338 has increased,and wall portions 390, 391, 392, 393, 394, and 395 of combustionchambers 360 are in direct heat transfer relationship with side walls336, 338. As an added benefit, with this configuration, the reduction ofexternal side wall area of combustion chambers 360 requires lessinsulation. This embodiment therefore improves heat transfer to thecooking medium and reduces manufacturing input costs, because lessinsulation is necessary for combustion chamber 360 at bends 386, 387,388, and 389. As used herein the terms “form” and “forming” refer to anymethod of altering and/or shaping side walls 336, 338 in order to recesscombustion chambers 360 into lower chamber 330, including weldingsectional pieces, forming by a brake press, and any other means thatallow combustion chambers 360 to be fitted within the recessed portionsof side walls 336, 338.

The embodiment of FIGS. 12 and 13 is substantially similar to theembodiment of FIGS. 10 and 11 , with the exception that vertical sidewalls 336, 338 of lower chamber 330 have been replaced with angled sidewalls 436, 438, which are sloped from top to bottom, thereby forming aV-shaped lower chamber 430 that is wider at the top than at the bottom.This configuration adds additional advantages, in that the interiorsurface area of lower chamber 430 is slightly increased and the volumeof lower chamber 430 is increased.

To promote ease of cleaning of lower chamber 430 and cold zone 345, therecessed channels of combustion chambers 360 are formed with slopedsurfaces and radius bends as opposed to sharp folds. The sloped surfacesare therefore easy to brush clean. Upward facing sloped portions 394,395, 396, and 397 of side walls 436, 438 are steep to promote foodparticles easily passing to cold zone 345 without settling on theinterior surfaces of side walls 436, 438. Sidewalls 436, 438 of lowerchamber 430 are tilted or sloped from vertical thereby increasing theopening to lower chamber 430, permitting better access for brushing orhand wiping around the recess areas. Angled side walls 436, 438 areeasily fabricated using typical sheet metal forming tools, such as acomputer controlled press brake.

It will be appreciated that the sloped side walls of lower chamber 430may also be used in alternative embodiments in which the combustionchambers are not recessed into angled side walls 436, 438. In suchalternative embodiments, side walls 436, 438 would be sloped butstraight. As such, combustion chambers 360 would be in heat transfercommunication with the exterior surfaces of side walls 436, 438, as withthe embodiment of FIG. 2 . Thus, lower chamber 430 would be wider in atransverse direction at an upper end where lower chamber 430 joinstransition zone 342, than at a lower end where lower chamber 430 joinscold zone 345.

Although combustion chambers 60 and 360 have been heretofore describedand shown affixed to side walls 36, 38, 336, 338, 436, and 438,respectively, it will be appreciated that additional combustion chambers60 and 360 may also be affixed to the exterior surfaces of transitionwalls 52, 54, 352, and 354 of transition sections 42 and 342, extendingfrom front walls 48 and 348 to back walls 50 and 350, respectively.

It is apparent that an invention with significant advantages has beendescribed and illustrated. Although the present application is shown ina limited number of forms, it is not limited to just these forms, but isamenable to various changes and modifications without departing from thespirit thereof.

What is claimed is:
 1. A deep fryer, comprising: a cooking vessel forholding a cooking medium, the cooking vessel comprising: a front wall; arear wall; a bottom wall; and opposing sidewalls; and a natural draftcombustion system comprising: at least one supply conduit for receivingand distributing a combustion gas; at least one burner in fluidcommunication with the at least one supply conduit; and at least onegenerally horizontal combustion chamber in fluid communication with theat least one burner, the combustion chamber forming a discrete enclosedchamber and being exterior to and in heat transfer communication with anexterior surface of one of the sidewalls; wherein each combustionchamber comprises: an inlet portion located near the front wall of thecooking vessel; and an outlet portion located near the back wall of thecooking vessel; and wherein the combustion gas flows continuously in agenerally horizontally orientation along a corresponding side wall ofthe cooking vessel from the inlet portion to the outlet portion.
 2. Thedeep fryer according to claim 1, wherein the at least one burnerincludes an angled portion.
 3. The deep fryer according to claim 1,wherein the at least one burner is generally straight.
 4. The deep fryeraccording to claim 1, wherein the combustion gas flows in response to anatural pressure differential between the combustion gas and thesurrounding atmospheric condition.
 5. The deep fryer according to claim1, wherein each combustion chamber is sealed.
 6. The deep fryer of claim1, further comprising: a baffle system disposed within each combustionchamber.
 7. The deep fryer of claim 1, wherein at least one of thecombustion chambers is recessed into a corresponding side wall of thecooking vessel.
 8. The deep fryer of claim 1, wherein each combustionchamber is formed by affixing a three-sided generally C-shaped member toan exterior surface of one of the side walls of the cooking vessel, suchthat such side wall serves as a fourth wall of such combustion chamber,thereby resulting in such combustion chamber being a closed chamber. 9.The deep fryer of claim 1, wherein each combustion chamber is generallyrectangular in a transverse cross-section.
 10. The deep fryer of claim1, wherein each combustion chamber is generally semi-circular in atransverse cross-section.
 11. The deep fryer of claim 1, wherein eachcombustion chamber is generally square in a transverse cross-section.12. The deep fryer of claim 1, wherein each combustion chamber isgenerally semi-elliptical in a transverse cross-section.
 13. The deepfryer of claim 1, wherein each combustion chamber comprises: a pluralityof zones disposed along the length thereof; wherein each zone isconfigured, such that selected gas combustion and heat transferfunctions, relative to the cooking vessel, occur in each zone.
 14. Thedeep fryer of claim 1, wherein the at least one burner is a plurality ofburners, with multiple burners on each side of the cooking vessel; andwherein the at least one generally horizontal combustion chamber is aplurality of generally horizontal combustion chambers, with multiplegenerally horizontal combustion chambers on each side of the cookingvessel.
 15. The deep fryer of claim 1, wherein the combustion chamberhas an upward draft angle relative to the horizontal from the inletportion to the outlet portion.
 16. The deep fryer of claim 1, whereinthe combustion chamber is tapered inwardly from the inlet portion to theoutlet portion.
 17. The deep fryer of claim 1, wherein each burner isangled downward such that a corresponding flame front of the combustiongas is biased toward a bottom of the corresponding combustion chamber.